Which of the following animal is devoid of notochord and nerve cord in...
The solitary ascidian Herdmania momus is one of the most commonly encountered species of ascidians. While commonly referred to simply as sea squirts, this name is ambiguous, as it can refer to any member of the sub-phylum Tunicata.
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Which of the following animal is devoid of notochord and nerve cord in...
Ascidians are marine invertebrates commonly known as sea squirts. They belong to the phylum Chordata, which includes organisms with a notochord and nerve cord at some stage in their life cycle. However, in the adult stage, some ascidians including Herdmania lose these structures.
Explanation:
Notochord:
- The notochord is a flexible rod-like structure found in the embryos of all chordates. It provides support and helps in the development of the nervous system.
- In some chordates, including amphioxus and vertebrates, the notochord persists into the adult stage.
- However, in some ascidians, the notochord is present only in the larval stage and is lost during metamorphosis into the adult stage.
- Herdmania is one such ascidian that lacks a notochord in its adult stage.
Nerve cord:
- The nerve cord is a tubular structure that runs along the dorsal side of the body in chordates. It is formed from the ectoderm and develops into the central nervous system.
- In some chordates, including amphioxus and vertebrates, the nerve cord persists into the adult stage.
- However, in some ascidians, the nerve cord is reduced or absent in the adult stage.
- Herdmania is one such ascidian that lacks a nerve cord in its adult stage.
Conclusion:
Hence, option A, Herdmania (Ascidian), is the correct answer as it is the only organism among the given options that lacks both notochord and nerve cord in its adult stage.
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